Tight control over the delivery of insulin in both type I diabetes (usually juvenile onset) and type II diabetes (usually late adult onset), has been shown to improve the quality of life as well as the general health of these patients. Insulin delivery has been dominated by subcutaneous injections of both long acting insulin to cover the basal needs of the patient and by short acting insulin to compensate for meals and snacks. Recently, the development of electronic, external insulin infusion pumps has allowed the continuous infusion of fast acting insulin for the maintenance of the basal needs as well as the compensatory doses (boluses) for meals and snacks. These infusion systems have shown to improve control of blood glucose levels. However, they suffer the drawbacks of size, cost, and complexity. For example, these pumps are electronically controlled and must be programmed to supply the desired amounts of basal and bolus insulin. This prevents many patients from accepting this technology over the standard subcutaneous injections.
Hence, there is a need in the art for a convenient form of insulin treatment which does not require significant programming or technical skills to implement to service both basal and bolus needs. Preferably, such a treatment would be carried out by an infusion device that is simple to use and mechanically driven negating the need for batteries and the like. It would also be preferable if the infusion device could be directly attached to the body and not require any electronics to program the delivery rates. The insulin is preferably delivered through a small, thin-walled tubing (cannula) through the skin into the subcutaneous tissue similar to technologies in the prior art.
While the idea of such a simple insulin delivery device is compelling, many obstacles must be overcome before such a device may become a practical realty. One problem resides in insulin supply. Patients vary greatly on the amount of insulin their device must carry to provide treatment over a fixed time period of, for example, three days. This is one environment where one size does not fit all. Another problem is with cannula deployment to support insulin delivery. Cannula deployment to support delivery of the insulin beneath the patient's skin must be made easy and convenient. This is not as easy as it seems because cannula deployment, as generally and currently performed in the art, requires insertion of a cannula carrying needle into the patient and then retraction of only the needle to leave the cannula in place beneath the patient's skin.
Still further, medical devices, such as IV pumps, insulin pumps and the like, designed to deliver liquid medicaments to patients by means of intravascular, intramuscular or interstitial injection are subject to problems due to difficulties in filling with the medicament prior to use. Specifically, the process of transferring a liquid medicament from a storage vial to the drug delivery device can be both difficult and error prone. The difficulty can be caused by the need to maintain sterility of the contacting surfaces, and the logistics of using an intermediate transfer device such as a syringe. Errors can be caused by miss-measurement of fluids and by the inadvertent introduction of air into the drug delivery device. While the difficulties can be inconvenient, the errors can result in more serious problems such miss-dosing. The consequences of incorrect treatment due to miss-dosing can vary from minor to serious. In the case of insulin delivery, incorrect dosing can lead to acute hypoglycemia or chronic hyperglycemia.
One currently proposed method of preparing a disposable insulin delivery device for use includes transferring insulin from a liquid medicament vial to the insulin delivery device. As proposed, this may be accomplished with a syringe and mounted needle by first drawing an amount of air into the syringe equal to the amount of insulin that will be withdrawn from the vial. Next, the vial septum is pierced with the needle and air is injected from the syringe into the vial, thus pressurizing the vial. The desired amount of insulin is then withdrawn from the vial into the syringe and thereafter, the needle is withdrawn from the vial. Next, the syringe is held in a vertical orientation to allow entrapped air to rise to the top. The syringe plunger is then gently advanced until the air has been ejected and a small amount of fluid is expressed from the syringe. The septum on the medicament delivery device is then pierced with the syringe to access the device reservoir and the insulin is injected into the reservoir. Lastly, the reservoir is inspected for air bubbles and those larger than 1 mm in diameter are removed by reinserting the syringe needle and aspirating the bubble.
This foregoing procedure is subject to error during the syringe filling and degassing steps, and during the reservoir filling step. Error during either step can result in excess air injected into the medicament delivery device. Excess air in the reservoir of the medicament delivery device can adversely affect the amount of insulin delivered to the patient during use, thereby compromising treatment.
Hence, there is a need for an improved filling device and method that will reduce the complications and potential errors associated with transferring a medicament from a storage vial to a drug delivery device. As will be seen subsequently, the present invention addresses these and other issues.